Work machines, in particular, earthworking machines, perform operations by controllably moving a work implement, such as a bucket or blade, to accomplish the desired function. The work implement is connected to the work machine in a manner that usually allows movement in multiple directions. Movement is normally accomplished by rotation of linkage members about a linkage point.
For example, a track-type tractor controls movement of a blade in several directions. As examples, the blade is lifted and lowered by pivoting a C-frame about a linkage point on the main frame; and the blade is pitched by pivoting a linkage point on the blade with respect to the C-frame.
As another example, an excavator work implement usually consists of a boom, stick, and bucket; each of which moves by rotating about a pivot point with respect to the component it is connected to. For example, the stick moves by pivoting about the linkage point where the stick and the boom are connected together.
It is often desired to monitor the rotating motions and angular displacements of these linkage points to determine the position of the work implement relative to the machine or to the terrain. Several methods for sensing and determining these types of motions are used, including the use of rotary position sensors, commonly known as resolvers. A typical resolver functions by having a first portion attached to a linkage pin, and a second portion attached to the housing surrounding the linkage pin. As the linkage pin rotates relative to the housing, the resolver senses the amount of rotation and provides an electrical signal indicating this value.
In earthworking environments, however, conditions are normally detrimental for sensors of this nature. For example, dust, dirt, mud, rocks, and severe shocks and vibrations are a normal part of earthworking operations. In addition, the unwanted forces acting on the linkage pins, such as radial and axial forces, are communicated to resolvers; thus degrading the accuracy and shortening the life of these sensors.
Attempts have been made to design rotary position sensors which resist the effects of earthworking environments. For example, isolation mounts have been used to mount the sensors to the linkage pin assemblies. However, the isolation mounts themselves are exposed to the elements, and failure of these components is common. In addition, radial and axial forces communicated through to the sensors are a significant factor in contributing to the common failures of the sensors.
The present invention is directed to overcoming one or more of the problems as set forth above.